1. Technical Field
The present invention relates to a damping system for suppressing (controlling) vibrations of a steering wheel which incorporates an airbag device.
2. Background Art
When vibrations are transmitted to a steering wheel in a vertical direction and a horizontal direction while the vehicle is being driven at high speed or an in-vehicle engine is idling, the comfortable driving of the driver may be deteriorated. For this reason, techniques for suppressing (controlling) the vibrations of a steering wheel have been developed and proposed. One of the techniques employs a dynamic damper including a damper mass and an elastic member which supports the damper mass on a metallic core frame of the steering wheel. According to this technique, when vibrations of a frequency which is the same as or close to a resonance frequency specific to the dynamic damper are transmitted from the steering wheel to the dynamic damper, the dynamic damper resonates to absorb the vibration energy of the steering wheel. The vibration of the steering wheel is then suppressed (controlled) by the absorption of the vibration energy.
Recently, the steering wheel incorporates therein an airbag device so as to protect the driver from impact produced when the vehicle is involved in a collision. The airbag device includes an airbag and an inflator for supplying a gas to the airbag. When the vehicle is involved in a collision, the airbag is inflated to the rear by supplying the gas into the airbag, whereby the driver is protected from the impact produced upon collision.
The airbag device occupies most of an interior space defined within the steering wheel. Therefore, in recent steering wheels, it becomes difficult to incorporate the dynamic damper in the steering wheel.
Patent Document 1 describes a steering wheel in which an airbag device is made to double as a dynamic damper.
This steering wheel includes a holder, an airbag module, an elastic body and a horn switch. The holder is fixed to a steering shaft which extends in a front-right direction. The airbag device is configured by attaching an inflator and an airbag to a bracket individually and is disposed on a rear side of the holder. The elastic body is formed into a ring shape and is mounted in a mounting hole formed so as to penetrate the bracket in the front-rear direction. The horn switch includes an annular slider which is disposed between a support member and the elastic member, and a horn unit is activated by a forward movement of the slider which occurs in association with a pressing operation of the airbag device.
Patent Document 2 also describes a similar damping system.
According to the steering wheel, the airbag device functions as a damper mass of a dynamic damper, and the elastic member functions as a spring of the dynamic damper. When the steering wheel vibrates in directions such as vertical and horizontal directions perpendicular to the steering shaft with a predetermined frequency, the elastic member vibrates together with the airbag device in directions perpendicular to the steering shaft while the elastic member is deformed elastically with a resonance frequency which is the same or close to the predetermined frequency, whereby the vibration energy of the steering wheel is absorbed. Accordingly, the vibration of the steering wheel is suppressed (controlled) by the absorption of the vibration energy.    Patent Document 1: JP-A-2009-202859    Patent Document 2: JP-U-2-38275